1. Field of the Disclosure
The present disclosure relates to a semiconductor light emitting device, and more particularly, to a nitride-based semiconductor light emitting device having an improved structure in which light extraction efficiency is improved, and a method of manufacturing the same.
2. Description of the Related Art
Light emitting devices, such as light emitting diodes (LED), are basically semiconductor PN junction diodes. The silicon PN junction plays a leading role in the electronic information revolution, and the PN junction of a III-V group compound semiconductor plays a leading role in the light revolution. A III-V group compound semiconductor is made by the combining of III- and V-group elements of the periodic table of elements. It has an advantage of luminous efficiency that is near 100%. This luminous efficiency is approximately one thousand times higher than that of silicon. Thus, LEDs are widely used in light emitting devices, such as a diode laser, from the initial stage of development of a material and play a leading role in the optical revolution. In addition, since LEDs have a higher movement speed of electrons and can operate at a high temperature, they are widely used in high-speed and high-power electronic devices. In particular, several III- and V-group elements are mixed with one another so that a semiconductor having a variety of material compositions and characteristics can be manufactured.
As basic characteristics of an LED, luminosity (units: candela (cd)) is used in an LED in a visible ray region and radiant flux (units: watt) is used in an invisible ray region. Luminosity is indicated by light velocity per unit cubic angle, and brightness is indicated by luminosity per unit area. A photometer is used to measure luminosity. Radiant flux represents all power radiated from all wavelengths of an LED and is indicated by the energy radiated per unit time.
A major factor for determining visible ray LED performance is the luminous efficiency indicated by lumen per watt (lm/W). This corresponds wall-plug efficiency (optical output/input electric power amount) in consideration of human eye luminosity factor. Luminous efficiency of an LED can be mainly determined by three factors, such as internal quantum efficiency, extraction efficiency, and operating voltage. Research for the improvement of the luminous efficiency is being currently conducted.
In general, conventional LEDs have a sapphire/n-GaN/MQW/p-GaN structure. However, in such LEDs, defect density is high due to the limitations of manufacturing technology. Thus, there are limitations when addressing current technical objectives, such as a first objective of improving the internal quantum efficiency of an MQW layer and a second objective of manufacturing a high-power LED. Accordingly, the structure of a LED needs to be improved so that the limitations can be overcome and the external extraction efficiency of light can be increased.